Close file to no leak file descriptor memory. Found by Coverity.
Return error if allocation of new element was not possible.

Found by Coverity.
Introduce InvalidCommandId.

This allows a 32-bit field to represent an *optional* command ID
without a separate flag bit.

Andres Freund
Show schemas in information_schema.schemata that the current has access to

Before, it would only show schemas that the current user owns.  Per
discussion, the new behavior is more useful and consistent for PostgreSQL.
Merge remote-tracking branch 'origin/master' into table_functions_record